The invention is in the field of high-intensity, high-temperature arc discharge lamps containing a metal halide gas, such as is disclosed in U.S. Pat. No. 3,259,777 to Elmer G. Fridrich. Such lamps are useful, for example, in photographic projectors and other optical devices requiring a compact high-intensity light source of high efficiency. The metal halide gas may be produced, for example, by a salt of iodide such as indium triiodide which converts to iodine gas due to the high temperature of the operating lamp. A starting gas, such as argon, can be included in the lamp to aid in starting.
In such a lamp, after it comes up to operating temperature, the inner tips of the tungsten electrodes are molten and vaporize, and the halogen gas in the lamp causes a regenerative cycle to occur which carries the vaporized tungsten back to the electrodes and prevents it from depositing onto (and blackening) the bulb wall, as is more fully described in the above-referenced Fridrich patent.
It has been found that a lamp of this type, if the arc discharge becomes disrupted momentarily, such as by a momentary interruption of current furnished to the lamp, cannot be restarted for a period of time, such as up to one minute or so. This is considered by some to be an undesirable characteristic of an otherwise highly desirable lamp, especially when used in motion picture projectors, and as reprographic lamps such as plate burner lamps in printing equipment.